The invention relates to a device and a method for production of medical fittings, in particular dental restorations. Dental restorations are here intended to cover both alloplastic and endoprosthetic/exoprosthetic fittings. In the dental field, these can be inlays, onlays, crowns, bridges, prostheses, implants or veneers.
EP 0,455,853 A1 discloses a device for production of medical, in particular dental, prosthetic fittings, with a receiver for a workpiece from which the fitting is produced. The receiver is connected to a workpiece spindle which is designed in such a way that the workpiece can be moved in the axial direction about a feed axis. For machining the workpiece, a first tool spindle is provided with at least one machining tool which can be set in rotation, the tool spindle being arranged and mounted in such a way that the at least one tool held by it can be moved toward and away from the workpiece perpendicular to the feed axis of the workpiece spindle. Moreover, a second tool spindle is provided which, as regards movement relative to the workpiece, is arranged and mounted in the same way as the first tool spindle, but preferably offset 180xc2x0 relative to the latter and driven separately. In addition, control means are provided which control the drive mechanisms of the tool receiver and of the tool spindles for simultaneous machining of the workpiece according to predetermined contour data.
By means of the two separately arranged and separately driven spindles for machining tools which can be set in rotation, it is possible to synchronize their movement with the movement of the workpiece and to machine the fitting to be produced practically simultaneously with two tools, as a result of which the work time for production of a fitting can be substantially reduced.
The two spindles lying opposite each other can be arranged in one plane, it being possible to choose between a horizontal arrangement of the spindles or an arrangement in which the spindles are perpendicular to the aforementioned plane or at an angle to it.
The simultaneous machining is carried out with a grinding wheel, driven by one work spindle, shaping the outer contours of the crown, and with an end-milling cutter practically following behind the grinding wheel. The end-milling cutter finishes or smoothes the surface and shapes the fissures which, because of the large radius of the grinding wheel, cannot be shaped by the latter.
The object of the invention is to find a tool combination and a method by which the shapes of medical fittings, particularly of typical dental restorations, can be formed especially quickly and with precision. In this connection, it is to be ensured that the fittings are not destroyed by the machining forces. It is also necessary for the tools to permit a simple construction of the machine. Finally, the tools are intended to permit efficient load control.
This object is achieved by the features of claim 1. According to the invention, the machining tools are designed as rods which can be set in rotation and have radial and terminal working faces. During machining of the workpiece, the machining tools are arranged at approximately the same height relative to the feed axis of the workpiece, so that they work along closely adjacent machining areas.
The fact that the machining tools work at approximately the same height prevents the machining forces from destroying the fitting. Also, because the workpiece is machined at approximately the same height, the machining time is kept short. By using rods which can be set in rotation and have radial and terminal working faces, the final geometries can be obtained in a single operating pass. A second pass is not needed.
The workpiece can preferably be advanced in the axial direction, so that the machining tools do not have to be moved in the axial direction. This permits a simple construction of the machine.
In order to produce height and depth differences in the fitting, it is advantageous if the machining tools can be moved toward and away from the workpiece, along a first machining direction perpendicular to the feed axis of the workpiece.
Moreover, in order to produce a circumferential contour, it is advantageous if the machining tools can be moved along the workpiece along a second machining direction essentially perpendicular to the feed axis of the workpiece and essentially perpendicular to the first machining direction.
To achieve efficient load control, it is advantageous for the first and second machining tools to be driven separately.
In order to coordinate the two machining tools, it is advantageous to provide control means which control the movement of the machining tools for simultaneous machining of the workpiece according to predetermined contour data.
The machining areas advantageously lie essentially perpendicular to the feed axis, which means that it is possible to dispense with additional adjustment mechanisms for the machining tools, since the workpiece is advanced sufficiently and the machining tools do not have to be adjusted in the direction of the feed axis. This does not mean that the machining tools do not move, but that the machining tools are only moved in accordance with a predetermined machining area, which, relative to the device, is always the same.
To avoid machining forces, it is advantageous if the machining areas lie at most one tool diameter from each other.
To permit a precise orientation of the workpiece within the device, it is advantageous if the workpiece can be rotated about the feed axis. Moreover, the formation of undercuts is at least in part possible.
In order to obtain the second machining direction, it is advantageous if the first and/or second machining tool can be moved about an axis of rotation arranged parallel to the tool axis. Alternatively, a linear spindle drive can also be provided, but this is more complicated in constructional terms.
The machining tools are advantageously spaced apart relative to the axis of rotation in such a way that the machining areas touch and/or at least partially overlap.
This can be achieved, for example, by the distances of the two tools from the respective axes of rotation being identical. If the distances are different, the position of the axis of rotation within the device can be changed so that the machining areas touch and/or at least partially overlap.
To produce a typical dental restoration, it is advantageous if one machining tool is a cylinder grinder and the other machining tool is a grinder rod tapering toward a point.
By means of the cylinder grinder, it is possible to sharply define the inner edges of a restoration. The top side of the restoration can be formed using a tapering grinder rod, and fissures can be produced with a high degree of detail and precision if the grinder rod, tapering toward a point, has a point radius of 0.1 to 0.5 mm and a cone angle of 15xc2x0 to 55xc2x0 . The control characteristics can also be governed in this way.
To form an undercut on the fitting, it is advantageous if at least one tool can be swiveled about a swivel axis in such a way that the first machining direction of the tool is arranged at an angle of less than 90xc2x0 relative to the feed axis of the workpiece.
The invention also relates to a method for production of medical fittings, in particular dental restorations, using a machining device with at least two simultaneously operating machining tools, the workpiece, during machining, being guided in the axial direction along a feed axis past the tools. According to the invention, the machining tools are designed as rods which can be set in rotation and have radial and terminal working faces effecting radial and/or terminal removal of material, and the machining tools are guided in closely adjacent machining areas on the workpiece and consequently work at approximately the same height relative to the feed axis.
The advantage of this method lies in the fact that the fittings are not destroyed by machining forces, and the special geometry of the machining tools permits timesaving machining.
Height and depth profiles can be produced by virtue of the fact that the workpiece, during machining, is guided in the axial direction past the tools, and at least one tool is moved toward and away from the workpiece in a first machining direction which is perpendicular to the feed axis of the workpiece.
The method is advantageously carried out with the workpiece being advanced in the axial direction, and the workpiece being rotated about the feed axis to form undercuts.
In order to completely machine the outer surfaces of the fittings, it is advantageous if the machining tools can impinge into the machining area of the other. machining tool.
In order to permit optimum time control of the machining tools, it is advantageous if the machining tools work in opposite directions in the area of the workpiece in which the fitting is produced. To ensure that the machining tools do not touch one another, safety control function is provided which leads to deflection of one of the two machining tools.
In order to form undercuts in the surface of the fitting, at least one machining tool can be swiveled about a swivel axis in such a way that the first machining direction of the tool is arranged at an angle of less than 90xc2x0 relative to the feed axis of the workpiece.
To avoid collisions of the two machining tools, the movements of the two machining tools are synchronized at the end of each machining area, by each machining tool leaving the trajectory assigned to it and by the faster machining tool waiting for the slower machining tool.
In order to produce a fitting which can be divided into an upper part and a lower part delimited by an equator line, one machining tool advantageously machines the upper part, and the other machining tool machines the opposite lower part of the fitting.
If the aim is to produce all the essential shapes of restorations of this geometry in one operating pass, it is advantageous to use a cylinder grinder for the lower part, and to use a grinder rod, tapering toward a point, to machine the upper part.